Adolescent: International Study of Built Environments and Physical Activity Numerous US and international health authorities recommend environmental and policy interventions for promoting physical activity (PA) and preventing obesity. Strategies should be evidence-based, but there are fewer studies of built environments in youth than adults. The evidence is weakened because studies underestimate effect sizes due to restricted range of environments. Adolescence is the time of steepest decline in PA, so this is a high-risk age group. To accurately assess the strength of association of the built environment attributes with PA, sedentary behavior, and weight status, greater environmental variability is required than any one country can provide. Thus, international studies are required, and the proposed IPEN Adolescent project is a coordinated study of built environments and PA, sedentary behavior, and obesity using common methods and based on: (a) our recently-completed NIH-funded TEAN study of adolescents in the US and (b) the IPEN Adult (International Physical Activity and Environment Network) Study, an ongoing 13-country study of adults coordinated by our team. Objective measures of PA and environments are especially important for studies of youth, and all countries in IPEN Adolescent will collect objective measures of PA, sedentary time, and built environments. Validated and systematically adapted surveys will assess built and social environment attributes, psychosocial and demographic variables, and additional outcomes (active transport to school, participation in organized sports and activity classes). The study is guided by a specific multi-level ecological model. At least 4680 adolescents aged 12-18 years, from 13 cities, in 9 countries will participate. Several countries already have data, and others will be funded for data collection. In each country, adolescent-parent pairs will be recruited from neighborhoods selected to vary in walkability and socioeconomic status. GIS- derived measures of walkability (community designs that support walking to destinations), playability (access to recreation facilities), and pedestrian accessibility (sidewalks, transit, barriers to walking) will be analyzed separately and combined into a physical activity-friendliness index. The primary aim is to estimate strengths of association between objective GIS-based measures of the community environment with accelerometer- measured PA and sedentary time in adolescents, from data collected according to a common protocol in at least 9 countries. The second aim is to estimate strengths of association between perceived measures of the community environment (NEWS-Youth survey) with self-reported walking/cycling to/from school and participation in youth sports and activity classes. The third aim is to estimate strengths of association between objective and perceived environment measures with overweight/obesity in adolescents (defined by international criteria). Analyses will adjust for multi-level clustering and individual demographics. All country investigators have experience with primary variables, and the Coordinating Center has experience ensuring data quality and comparable methods in international studies